Field of Invention
The present invention relates generally to sensors for implantation within a living animal and measurement of a concentration of an analyte in a medium within the living animal. Specifically, the present invention relates to sensors having a polymer graft including indicator molecules on the surface of the sensor body, where the opacity of the graft does not vary over time.
Discussion of the Background
A sensor may be implanted within a living animal (e.g., a human) and used to measure the concentration of an analyte (e.g., glucose or oxygen) in a medium (e.g., interstitial fluid (ISF) or blood) within the living animal. The sensor may include a light source (e.g., a light-emitting diode (LED) or other light emitting element), indicator molecules in a graft, and a photodetector (e.g., a photodiode, phototransistor, photoresistor or other photosensitive element). Examples of implantable sensors employing indicator molecules to measure the concentration of an analyte are described in U.S. Pat. No. 6,330,464, which is incorporated herein by reference in its entirety.
The sensor may include indicator molecules embedded in an opaque polymer graft (i.e., layer or matrix). For example, in an implantable fluorescence-based glucose sensor, fluorescent indicator molecules may reversibly bind glucose and, when irradiated with excitation light (e.g., light having a wavelength of approximately 378 nm), emit an amount of light (e.g., light in the range of 400 to 500 nm) that depends on whether or not glucose is bound to the indicator molecule.
A light source (e.g., light emitting diode (LED)) may emit the excitation light, which may then be absorbed by the indicator molecules in the polymer graft. A portion of the absorbed excitation light may be reflected from the polymer graft back into the sensor, and a portion of the absorbed excitation light may be emitted by the indicator molecules at a higher wavelength. The reflected and emitted light (e.g., fluorescent light) may be absorbed by one or more photodetectors within the body of the sensor.
Error may be introduced into analyte readings taken by a sensor as conditions of the sensor change over the life of the sensor and/or conditions or the sensing medium (e.g., protein concentrations in interstitial fluid) change over time. Thus, there is presently a need in the art for improvements to reduce the introduction of error into analyte readings taken by an implanted sensor.